Annealed shell



Aug. 31, 1948.

w. F. REAGER mummn swam.

'FnedoctQ 22, 1943 INVENTOR ATTORNEY Patented Aug. 31,}848

Application October 22, 1943, Serial No. 507,267

I '3 Claims.

The present application relates to explosion initiators oi the bursting type.

An object of the present invention is to provide an improved explosion initiator.

Another object oi the invention is to provide an improved squib.

Ajiurther object of the present invention is to provide an explosion initiator in which the initiating iorceis directed in a desired manner.

A still further object of the present invention is to provide an explosion initiator which is easily rupturable.

Still another object of the invention is to provide an explosion initiator in which the initiating force is localized and controlled.

Another object of the invention is to provide an explosion initiator which at the same time is easily rupturable and will tenaciously hold a initiating action. Generally, initiator shells are drawn to the form desired with integral bottom portions against which the explosive charge is loaded. but other methods oi working to shape,

.such as stamping, for example, may be employed.

Prior art explosion initiators have often given difilculty in that the initiating force has not been controlled in direction. This tendency has been particularly noticed in connection with electric squibs which contain a plug seal at the top end.

. Such plugs have often tended to blow out, permitting the initiating force to escape out the top rather than bursting the shell of the initiator as is usually desired. The present invention will be place and seal the end of shell ii. Sealing composition 2i is held in place by bead l5. Inside shell ll above charge it and connected to leg wires I1 and i9 is located electric fuse-head assembly 23. In operation leg wires ll and I! are connected to a source of electric current which fires fusehead 23 which in turn ignites charge l3. Charge is then bursts shell ii and fires an explosive to be initiated.

Numerous modifications oi the electric initiator shown are, oi course, possible as is well known in the art. For example, theshell may be made of materials other" than aluminum. Initiating charge it which is represented in the drawing as a single charge of black powder may, instead,

be in the form oi a plurality of separate charges iusehead 28, other suitable igniting means, such as bridge wires or spark gaps, with such flash compositions as may be desirable, may be employed.

As has been indicated above, it is usually desired that the initiating force be directed out through the initiator shell. Various methods of assuring this action have been proposed in the prior art. For example, one proposal has been to score the initiator shell so as to weaken it at the scored places and thereby make it easier to specifically illustrated in connection with electric squibs.

The drawing shows a view of an electric squib partially in section.

The squib is shown in generally conventional form. Drawn aluminum closed end shell Ii contains in its lower or closed portion an initiating charge I; of black powder. Shell ii is supplied with a bead is near its top or open end.' Leg wires l1 and I! for application to a source 0! current extend through sealing compositions 2| and Y 22, made of sulphur and asphaltic waterproofing composition respectively, which hold them in rupture. This method, while operative, is difilcult to perform in that it is quite a problem to control the depth of the scores and to insure that they are sufllcient to provide adequate rupturability but do not puncture the shell completely. A second method. useful for squibs, that has been suggested is locating a small portion of detonating explosive in the bottom of the squib near the initiating charge and adjacent the shell. The detoirating explosive opens a hole in the shell for the escape of the burning discharge from'the squib. This method is clumsy, adds considerably to the difilculty of manufacturing squibs, and makes squibs more dangerous because of the detonating explosive which must be included in them. A third method also applicable to squibs is to employ a heat-producing charge which melts the shell wall. This method, of course, has the disadvantage that a special charge must be employed.

According to the present invention, an initiator 3 i is provided which may employ ordinary and conventional charges, but which at the same time has a shell readily rupturable at any desired point, by providing a limited area of the shell relatively and materially softer than remaining areas of the shell. In a preferred embodiment of the invention, a local portion of the shell is annealed to a softened condition while remain ing portions are left hard. In this way, a place of easy rupturability is provided through which the initiating force may be directed.

For example, drawn shell ii of the initiator shown in the drawing is, before being charged with explosive, annealed adjacent the portion to be charged, making that portion soft so that the squib name will burst the shell and discharge therethrough, while the top portion of the shell is left hard and strong so as to provide an eflicient grip on the sealing plug and prevent its blowing out with consequent dissipation of the initiating force in the wrongdirection.

The annealing operation may be conducted in any convenient manner. The temperature and time necessary depend upon the particular material involved and the amount of workin which it has undergone while being shaped. They will also, of course, further depend upon the particular softness which it is desired to achieve. general, the higher the temperature, the shorter the time needed. For any particular Job, conditions for annealing are easily found. When annealing, care should be maintained to insure that the portion of the shell which it is desired to keep hard does not become so heated by conduction that it is also annealed. While such a portion may be externally cooled, it is often suflicient that the annealing be performed rapidly, for in that way it is possible that the desired portions may be softened before remaining portions become heated. With drawn aluminum shells, which have been found especially adaptable to the present invention, the annealing operation may be carried out by simple heating of the portion of the shell, which it is desired to soften, in a Bunsen flame for about a second. Other material, as indicated above, requires heating to a different temperature and/or time, and may also require quenching procedures. Gliding metal is an example of a metal which requires a higher temperature of anneal. Instead of metals, plastic materials which have been locally softened ,thickness, were annealed by passing the shells in may be used in some embodiments of this invention. For example, vinylidene chloride polymers, which may be work-hardened, have many of the properties of metals and may be formed and annealed to produce initiator shells according to the present invention.

Desirable directed rupturing of aluminum electric squib shells and adequate prevention of plug blowouts has been obtained when the top portions of the aluminum shells have been kept at a hardness as low as 8 as determined by means of a Shore scleroscope having a magnifier hammer. and when the softened portions have a hardness as high as 5. The parts of the shells extending about one-quarter inch down from their tops are considered to be top portions. If the hardness of the top portions of the shells is permitted toget lower than about 8 and the hardness of the softened portions is greater than about 5, plug blowouts occur under severe conditions of operation. It is possible by the use of more concentrated flame playing on a small area to obtain softened portions having a hardness considerably below 5, while retaining the desired hardness at the tops.

. 4 In fact, better results have been obtained when the softened portions show hardnesses of about 2 /2 to 3. Usually, it is desirable that hardnesses .of much below 2 be avoided as attempts to lower explosive action at the point of softenin takes place.

The invention will be more specifically illustrated by the following examples. In each of these examples, drawn aluminum shells, each of which was about 2% in. long. about 0.275 in. in outside diameter, and about 0.006 in. in wall an inverted position past two gas-oxygen torc es simultaneously directed horizontally against them. The torches were fed by propane gas from a cylinder, and oxygen at a pressure of about 2 lbs. per sq. in. The shells were moved intermittently so that each was acted on by the flame for a period of about four-fifths second. Immediately after passing through the flame, a Jet of air was directed against the tops of the shells and the shells were permitted to cool. A number of each batch were spread open, flattened, and their hardnesses measured in different portions with a Shore scleroscope, using the magnifier hammer. Other of the shells were charged and sealed to prepare electric squibs in the conventional form heretofore described. Each squib contained a charge of black powder, reaching about one inch from the bottom of the shell.

Example 1 A number of shells were annealed with the showed blowouts and none showed loose plugs.

The temperature of -60 F. was selected for coolg ing because it represents a particularly severe test condition for electric squibs.

Example 2 squibs prepared from shells unannealed, but otherwise similar to those of Example 1, were similarly fired after cooling to 60 F. Of these, the plugs of 25 blew out.

Example 3 Example 4 A number of shells were again prepared, but this time only one flame was used and it was adjusted so that the annealed portion was cut down to a spot about A in. in diameter. This spot was located about 1 in. from the bottom of the shell. The annealed portion showed a hardness of 2 to 4, and the top portion showed a hardness of 8 to 10. 25 squibs prepared from these shells were fired after cooling-to 60 F., and no blowouts or plug loosenings occurred. It was noted that a number of the shells on firing opened only in the area represented by the softened spot. When soft portions of greater area were prepared, the shells usually opened in about a /2 in. band almost completely around the circumference.

Example 5 Shells were prepared as in Example 4, but this time the annealed spot was softened to a hardness of only 5 to 6. The top portion again showed a hardness of about 8 to 10. Out 01 21 squibs prepared with these shells and fired after cooling to 60 F., 5 plugs blew out and 3 were loose.

Example 6 Example 7 A number of shells were annealed so as to produce a in. band ending 1 in. from the bottom of the shell. The softened bands showed a hardness of about 2-3, while the top portion of the shells maintained a hardness of about 8-10. Of 50 squibs prepared from such shells, one plug blew out on firing after cooling to 60 F.

The invention is not to be considered as necessarily being limited to the specific embodiments disclosed. For instance, it is not necessary that the annealing operation be performed by means of a hot flame or that the cooling operation when employed be performed by an air blast. Other sources of heat as electric heating, for example, may be employed, and also any suitable cooling media may be employed if desired.

Also, the invention need not be restricted to aluminum shells or squibs, but is applicable in its broader aspects wherever directed initiation is desired, and it is also applicable to other types of initiators, such as detonators, and to other types of shells.

The invention will further be found applicable to initiator shells which have been given a partial overall anneal. It is necessary only that there be hardness which can be locally annealed.

In the claims where hardnesses are mentioned, it is to be understood that they are Shore scleroscope hardnesses measured with the magnifier hammer and determined on shells which have been opened and unrolled into a flattened condition.

What is claimed is: I

1. An electric squib which comprises a drawn aluminum shell having a closed bottom, an explosive charge in said shell, a portion of said shell adjacent the top portion of said charge being annealed to a soft condition, and a sealing composition closing the top of said shell.

2. An electric squib according to claim 1 in which the top portion of the shell has a hardness no less than about 8 and in which the soft portion has a hardness no greater than 5.

3. An electric explosion initiator which comprises a drawn metal shell having a closed bottom, an explosive charge in said shell, and a seal closing the top of said shell; a portion of said shell adjacent said explosive charge being annealed to a soft condition so as to provide a place of easy rupturability through which the initiating force m'ay be directed.

WILLIAM F. REAGER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

